A phrase used generally to replace the name of someone when you have forgotten who you were going to talk about. This is similar to What's his face? or What's her face?, but usually catches the other person off guard.

Guy 1: So what are you doing for Labor Day this year?
Guy 2: Oh you know, I'm going home to play a game of football with what's his nuts, the guy who always ran an extra mile after gym practice.